Autogeneous fusion welds made by a high energy beam, such as an electron beam or laser beam, usually exhibit a triangular melt zone A (in cross-section), such as shown in FIG. 1, for most process speeds selected. The upper head B of the weld is usually wider (width C) than the width (D) of the welding beam (E) itself; this is due to heat conduction from the super-heated melt which is produced in the actual beam impact area with the workpiece. As the beam burns its way through the material, it creates the triangular heat affected zone as a function of time. As a consequence of the triangular cross-section of the melt zone A, the shrinkage during solidification of the weld is not uniform. If two unrestrained plates (10-11) are joined in this way, the weldment 13 causes warpage away from plane 14, as shown in FIG. 2. If the plates are restrained as in a box structure, warpage cannot take place, but high internal stresses will develop. Such stresses will be very high at the broad side of the triangular fusion line weld and can lead to weld failure.
It would be advantageous if the high energy radiant beams can be controlled during welding so as to produce a parallel-sided fusion weld zone, thus eliminating or reducing warpage and peak stresses in the weldments.
I am unaware of any publication which teaches the control of high energy radiant beams to obtain a parallel-sided heat affected or fusion weld zone. Particle beam control in the prior art has included optical focusing of lasers for rectilinear pattern control (see U.S. Pat. No. 3,965,327) and has included the use of masks over the workpiece to eliminate need for precise optics (see U.S. Pat. No. 3,742,182). These patents fail to disclose a means of oscillating the beam in a manner to obtain a parallel-sided melt zone. In Japanese Pat. Nos. 54-101596 and 54-116356, there is utilized an oscillating beam control to obtain a sinusoidal or spiral pattern for the print of the heat affected zone, but they do not teach how to obtain parallel-sided weld or melt zones. All of the melt or heat affected zones of these patents contain the typical and conventional V-shaped cross-section because the teachings do not provide anything that would compensate for such shape.